The present invention relates to an arrangement for supplying energy and a method for supplying energy.
The use of fuel cells for generating electrical current by oxidation of oxygen is widespread known and is used in different areas. The storage or retention of hydrogen, which is, as known, extremely explosive in the presence of oxygen, is an essential and critical aspect when using fuel cells.
Until now, a series of hydrogen storage methods were investigated: adsorptive, absorptive, as liquid, as highly densed gas. The disadvantage of all methods is their low energy density per volume and in part high costs of the carrier.
The so far common methods for storing hydrogen as liquid and under pressure represent technical solutions which so far—in particular due to their high technical effort and the high costs related therewith—do not exist in the public accessible area and not at all in isolated buildings as for example private buildings, holiday buildings, commercially used real estate or production buildings.
Containers with compressed hydrogen are difficult to seal and hydrogen explodes or detonates with pressure waves>1000 m/s in almost each mixture of 4-75% with air. Furthermore, the minimal ignition energy is lower compared to other gaseous compounds. Hydrogen is rated as extremely flammable (F+) and can spontaneously combust at high outlet velocities, such is the case also with other gases. The formula conversion when exploding with air is with 286 kJ/mol very high.
It is thus desirable to provide a technology for the energy supply using fuel cells, which avoids the risks of pure hydrogen.
Alternative storage means for hydrogen are known. Different aromatic compounds, in particular condensed polycyclic hydrogens are described in EP 1 475 349 which are usable for application as hydrogen storage. The substances described here are in particular used in mobile systems.
The basis of the mode of action of condensed polycyclic hydrocarbons, which comprise an extended π-conjugated electron system, is their property to undergo a hydrogenation reaction at moderate temperatures in the presence of a suitable catalyst. Thereby hydrogen is integrated into the substance (hydrogenated) with saturation of the unsaturated double bonds.
The hydrogen integrated by hydrogenation can be again obtained from the hydrogenated product by regenerating the aromatic substance in the back reaction merely by temperature increase and/or reduction of the hydrogen pressure.
It is exemplarily pointed to the hydrogenation/dehydrogenation of N-Ethylcarbazol (NEC). Hereby N-Ethylcarbazol (NEC) as educt is converted to the perhydro-form (H12-NEC) according to the following reaction scheme.

The storage density of hydrogen in this reaction is by volume about double as high as in case of a 700 bar tank filled with hydrogen.
The energy supply by solar cells is currently the most attractive possibility for the generative energy supply for isolated buildings such as private buildings, holiday buildings, commercially used real estate or production buildings. No other technology allows the renewable electricity generation with a variable power range of a few watts up to multiple MW. The integration of solar cells into the housing area is a common technology and depending on the location, roof area and orientation systems up to 30 kW peak power are common practice.
Although solar cells are the most attractive form of renewable electricity generation this technology has the disadvantage that the produced electricity cannot be intermediately stored over a longer period of time—also not in batteries due to the high storage costs and the low capacity—but has rather to be immediately consumed or to be fed into the grid. This is due to the law concerning renewable energies (EEG) of interest for the user, however provides additional burden to the electricity grid which is already under high stress.
A cost efficient possibility to store photovoltaic electricity in a medium term, e.g. for a few days up to a few weeks, is therefore an essential step in order to allow a further growth of the photovoltaic electricity generation.
The production of hydrogen by photovoltaic electricity is at present a commonly discussed option.
In order to achieve a high efficiency of the complete system an efficient coupling of the solar cells to the electrolyser, in which water is split to hydrogen and oxygen, is crucial. Hereby is to be evaluated if peek currents are of more advantage or rather a constant current supply over a longer period of time, but on a lower level. The option of a fast electricity storage for compensating peeks or fast declines for instance during cloudiness may crucially contribute as well as the selection of suitable cell technology which does not cause a complete turn off of the module for instance in case of a partial shadowing.
Some suggestions or models for the coupling of the photovoltaic with the generation of hydrogen are known. In EP 718 904 A1 is for instance a fuel cell system described which is a complete enclosed ensemble, and unifies the PEM fuel cell and a PEM electrolyzer. Herewith the requirement for a simple and cost efficient system is fulfilled. The electricity supply of the system takes places by means of the regenerative energy source provided with regenerative energy sources as for instance solar and/or wind energy.
The structure of the suggested fuel cell system allows a long life time and is designed for continues 24 hours operation. The goal is a service as simple as possible and no maintenance. An intelligent control controls fully automatic the immediate change of operating mode from hydrogen production to electricity production. Thereby the optimum operation point of the characteristic of the regenerative energy source and the PEM fuel cells/PEM electrolyzer is considered.
The PEM-electrolyzer requires distilled water for operation. The system regulates automatically the water balance required by the PEM electrolyser from a storage container provided therefore.
The described fuel cell system comprises also a hydrogen storage, which is designed in form of a metal hydride storage. This storage is made of specific metal alloys and allows the intermediate storage of gaseous hydrogen. The metal hydride storage can be filled with hydrogen in proximity to the ambient pressure.
The use of metal hydride storage as hydrogen storage is however less suitable for use in private households. They are expensive, often inefficient and have a series of intrinsic safety problems.